Answer
$z$ varies directly with $x$.
$z=kx$ ; $k = \dfrac{b}{a}$ is a constant
Work Step by Step
When $x$ varies inversely with $y$ then we have $y=\dfrac{a}{x}$; $b$ is a constant of variation.
When $y$ varies inversely with $z$ then we have $z=\dfrac{b}{y}$; $b$ is a constant of variation.
Thus, we have $z=\dfrac{b}{a/x}=\dfrac{b}{a}x$
Hence, we have found that $z$ varies directly with $x$.
That is, $z=kx$ ; Here $k = \dfrac{b}{a}$ is a constant
